Novel Mg7Ga2GeO12 microwave dielectric ceramics with ultralow-loss and low-permittivity for high-frequency packaging substrate

Novel low-permittivity Mg 7 Ga 2 GeO 12 ceramics with unique crystal structure consisting of rock-salt and β -Ga 2 O 3 blocks were prepared by the solid-state method. When sintered at 1380 °C, it showed ultra-high Q × f = 145,000 ± 300 GHz, low ε r = 10.5 ± 0.1, and τ f = −50.7 ± 1.0 ppm/°C. The positive deviation between the ε r and ε r (C–M) (8.7) of 21.2 % was due to the underestimating dielectric polarizability. The Phillips-Van Vechten-Levine (P-V-L) theory results indicated that the (Mg4/Ga1)-O bond had the greatest impact on the ε r and thermal stability, while the (Ga5/Ge1)-O bond mainly contributes to lattice energy. The intrinsic dielectric properties were analyzed by infrared reflectivity spectra. To demonstrate its potential for practical applications, a dielectric resonator antenna (DRA) based on Mg 7 Ga 2 GeO 12 ceramic was designed and fabricated, exhibiting a high gain (6.6 dBi) and radiation efficiency (> 98.3 %).